Photonic networks are networks that depend solely on optical techniques (without converting an optical signal into an electrical signal) to implement network functions such as transmission, multiplexing, demultiplexing, switching, and path control. Even before the rise of the photonic networks, optical fibers have been used for transmission paths and optical amplifiers have been used for amplifying a signal, but circuit switching has only been electrically achievable. More specifically, the optical signal has had to be converted into an electrical signal. Thus, a communication capacity in the network is limited by the performance of a switching apparatus.
The electrical switching involves extremely large power consumption in the apparatus, which increasingly rises with a higher communication speed and a larger number of systems of transmission paths that can be contained. To satisfy the demand for achieving both high speed communications and low power consumption growing by time, optical switching techniques achieving the switching by directly using the optical signal, without the need of the conversion into an electrical signal, have currently been under vigorous study and development.
FIG. 4 is a diagram illustrating the configuration of a wavelength multiplexer 900 (colorless/directionless/contentionless reconfigurable optical add/drop multiplexer (CDC ROADM)) according to a known optical switching technique. The wavelength multiplexer 900 is connected to WDM routes 901, 902, and 903 as a plurality of systems of optical fiber lines, and inputs and outputs an optical signal to and from each WDM route.
Each WDM route inputs and outputs a signal to and from the transponders 921, 922, and 923 through a split-and-select module 910. The transponders 921, 922, and 923 convert an electrical or optical signal transmitted from each client into an optical or electrical signal. Paths between the split-and-select module 910 and each of the transponders 921, 922, and 923 are referred to as a client contained path.
In FIG. 4, the three systems of WDM routes 901, 902, and 903 and the three systems of transponders 921, 922, and 923 are illustrated due to the limitation in the sheet size. Larger numbers of WDM routes and transponders may be connected to the actual wavelength multiplexer 900. Furthermore, the number of systems needs not to be the same between WDM routes and transponders.
The split-and-select module 910 includes: optical couplers 911 corresponding to optical signals transmitted and received by the WDM routes; and optical switches 912 corresponding to optical signals transmitted and received by the transponders. Each optical signal received from the WDM route 901 is split by a splitter 901a and each optical signal obtained by multiplexing in a multiplexer 901b is input to the WDM route 901. Similar splitters 902a and 903a and multiplexers 902b and 903b are respectively connected to the other WDM routes 902 and 903.
The optical signals output from the splitter 901a of the WDM route 901 are input to the optical coupler 911a, the multiplexer 902b of the WDM route 902, and the multiplexer 903b of the WDM route 903. Similarly, the optical signals output from the splitter 902a of the WDM route 902 are input to the optical coupler 911b, the multiplexer 901b of the WDM route 901, and the multiplexer 903b of the WDM route 903. The optical signals output from the splitter 903a of the WDM route 903 are input to the optical coupler 911c, the multiplexer 901b of the WDM route 901, and the multiplexer 902b of the WDM route 902.
The multiplexer 901b of the WDM route 901 multiplexes the signals output from the optical coupler 911d, the splitter 902a of the WDM route 902, and the splitter 903a of the WDM route 903, and outputs the resultant signal to the WDM route 901. Similarly, the multiplexer 902b of the WDM route 902 multiplexes the signals output from the optical coupler 911e, the splitter 901a of the WDM route 901, and the splitter 903a of the WDM route 903, and outputs the resultant signal to the WDM route 902. The multiplexer 903b of the WDM route 903 multiplexes the signals output from the optical coupler 911f, the splitter 901a of the WDM route 901, and the splitter 902a of the WDM route 902, and outputs the resultant signal to the WDM route 903.
The optical switches 912a to 912c each select one of the optical signals output from the multiplexers 901b to 903b of the WDM routes 901 to 903, and input the selected signal to the transponders 921 to 923. The optical switches 912d to 912f each select one of the splitters 901a to 903a of the WDM routes 901 to 903, and outputs the optical signal output from the transponders 921 to 923 to the selected destination.
When an optical signal output from the splitter 901a of the WDM route 901 is to be received by the transponder 921, the optical switch 912a may select the optical signal transmitted from the optical coupler 911a, so that a drop path will be established. When an optical signal is to be transmitted to the multiplexer 901b of the WDM route 901 by the transponder 921, the optical switch 912d may select the optical coupler 911d as the destination of the output optical signal, so that an add path will be established.
The inventors of the present invention have already put such a wavelength multiplexer 900 into market in 2011 (NPL 2) as an apparatus supporting 100 Gbit/s Ethernet (registered trademark), and the apparatus is currently under technical development to achieve higher speed and larger capacity.
Technical literatures related to the apparatus include: PTL 1 describing an optical node system that can achieve function enhancement and troubleshooting in a network at a low cost by using n×n optical switches; NPL 1 introducing recent trends in the photonic network described above; and NPL 2 describing the wavelength multiplexer supporting 100 Gbit/s Ethernet that has been put into market by the inventors as described above.